Temperature control system



March 10, 1970 B. H. PINCKAERS TEMPERATURE CONTROL SYSTEM Original FiledJan. 26, 1968 n Y R m M M m. w J m VHN W WMH A M W H a T M Y .llll l l II I l I I I I I I I I I I I l lm llmll hi M31 n n u u n n 5 u .z m n mmm u u n m u 408i L mm. nEO m 6 u E :7 2W m 1 2mm? 0 mm II N \QIMII \0 vmm o 0 S w mm n u u n United States Ratent O 3,499,482 TEMPERATURECONTROL SYSTEM Balthasar H. Pinckaers, Edina, Minn, assignor toHoneywell Inc., Minneapolis, Minn, a corporation of Delaware Originalapplication Jan. 26, 1968, Ser. No. 700,770. Divided and thisapplication Feb. 19, 1969, Ser.

Int. Cl. F25!) 29/00 U.S. Cl. 165-24 4 Claims ABSTRACT OF THE DTSCLOSUREA solid state temperature control system that uses a bridge network tocontrol transistor circuits that operate a heating fuel valve or acooling relay. The selection of a heating or cooling mode of operationis made by a manual switch on a subbase at the thermostat. The operationis in turn controlled by the use of feedback circuits between thetransistor circuits and the bridge.

This is a division of application Ser. No. 700,770, filed Jan. 26, 1968.

BACKGROUND OF THE INVENTION The present invention is directed to atransistorized temperature control system that utilizes a thermostathaving no switching contacts and one which has a tempera ture responsivecircuit that can be used for both heating and cooling.

Basically the present invention utilizes temperature responsive circuitmeans in the form of a bridge circuit including a thermistor thatcontrols a transistor amplifier arrangement to in turn operate a fuelvalve or a cooling relay. A feedback circuit means is utilized so thatthe bridge and thermistor are capable of providing both an ofiF-on andmodulating control of the fuel valve for continuous variation of theheat supplied to a space being controlled.

A changeover switch is provided in a subbase for the thermostat whichallows switching the thermostat from a heating to a cooling control modeby merely changing the feedback circuits which interconnect thetransistor amplifier and bridge. This change also provides the necessarychange in mode of operation of the transistor amplifier so that itswitches the cooling relay associated with the cooling equipment.

BRIEF DESCRIPTION OF THE DRAWING The single figure discloses a circuitdiagram of a complete temperature control system for a controlled spacewherein a thermostat, subbase, fuel valve, cooling relay and powersupply make up the entire system.

DESCRIPTION OF THE PREFERRED EMBODIMENT The temperature control systemis made up of a number of individual units that are mounted atconvenient 3,499,482 Patented Mar. 10, 1970 locations in a conventionalmanner. The system includes a thermostat means 10, and a subbase 11,upon which the thermostat is mounted when the system is used for bothheating and cooling. A fuel valve means 12 controls the flow of fuel toa furnace, not shown. A cooling relay means 13 contains the controlelements for operating a refrigeration compressor, not shown, forcooling. The final element making up the overall system is a powersupply means 14 which is connected to a conventional source of power 15for supplying the necessary voltages for operating the temperaturecontrol system. The thermostat means 10, subbase 11, fuel valve means12, cooling relay means 13, and power supply means 14 will eachindividually be described as to their makeup before the overalloperation of the system is described.

Thermostat means 10 includes a temperature responsive circuit means inthe form of a bridge network including calibrating potentiometer 16,resistor 17, resistor 18, resistor 20, a set point potentiometer 21, anda pair of parallel resistors 22 and 23. Resistor 23 is a temperatureresponsive element or negative temperature coefficient thermistor whichactually does the sensing of temperature of the controlled space tochange the bridge network output as a function of the temperature.Further included in the bridge are a pair of transistors 24 and 25 thatare connected through resistors 26 and 27 to form along with resistor 28an amplified output for the bridge at terminals 30, 31. The state ofbalance of the bridge changes the conduction of transistors 24 and 25thereby changing the voltages appearing at points 30 and 31 to in turnchange a bias to a third transistor 32 that forms a controlled outputfrom the bridge depending on the value of thermistor 23. Transistor 32in turn is connected by conductor 33 to a capacitor 34 and a voltagedivider network made up of resistors 35, 36 and 37. As the conduction oftransistor 32 changes due to a difference in potential across points 30and 31, a varying voltage appears across the voltage divider made up ofthe resistors 35, 36 and 37. The last named resistors make up a voltagedivider output means for the bridge or temperature responsive circuitmeans. This output is amplified by additional transistors.

A transistor 40 has its base-emitter circuit connected across resistor37 and has its collector connected by conductor 41 to heat anticipatorresistor 42 to a conductor 43 that supplies power to the thermostatmeans 10 from the power supply means 14. The power supply means 14 alsosupplies power on conductor 44. A transistor 45 has its base-emittercircuit connected across resistor 36 and has its collector connected byconductor 46 and resistor 47 to conductor 43 to obtain power for itsoperation.

A third transistor 50 has its base-emitter circuit connected across thetransistors 40 and 45, through a diode 51 and in turn has its collectorconnected by conductor 52 to a conductor 53 that provides a conductionpath from the power supply means 14 through other components as will bedescribed, and provides a path through resistor 54 that forms a negativefeedback path to the base of transistor 25. A positive feedback path isprovided within the thermostat means 10 by conductor 55 and resistor 56that connect the collector of transistor 40 to the base of transistor25. A third feedback circuit is provided within the thermostat means 10by conductor 57 and resistor 58 through the associated subbase means 11on conductor 59. This feedback circuit provides a positive feedback fromthe collector of transistor 50 via the subbase 11 (during one phase ofoperation) through the resistance 58 and conductor 57 to the base oftransistor 24 for a function that will be brought out during a discussion of the operation of the system.

The collector of transistor 40, in addition to being connected toconductor 41, is also connected to conductor 60 to provide an outputcircuit for the transistor 40 through subbase means 11. A resistor 61forms the last component in the thermostat means and is connectedbetween the conductors 53 and 44 to shape or balance the internaldissipation of transistor 50.

The subbase means 11 is a mounting means for thermostat means 10 whenboth heating and cooling modes are used. In order to obtain the heatingor cooling function a manual switching means 62 is provided. In theposition shown in the drawings, the manual switching means 62 is in theheat position. The switching function is accomplished by a pair ofshorting bars 63 and 64 which slide across .a group of terminalsshorting them in sequence. In the position shown, the upper terminalsare shorted by the bars 63 and 64. As the manual switching means 62 ismoved to the off or center position, the center pair of terminals areshorted by the bars 63 and 64. In the cool position, the bars 63 and 64short the lower two terminals of each of the groups of four shown. Thistype of switch-. ing is conventional and it is only necessary tounderstand that shorting bars 63 and 64 change a function upon a manualchange of their position. A second manual switching means 65 has beendisclosed with a shorting bar 66 to provide an automatic and on controlof a fan, not shown, in the cooling equipment. Switch 65 in the Autoposition shown provides an open circuit to a conductor 67 from theconductor 68 and removes the fan relay 86 from operation. When the bar66 is moved to its on or lower position, the conductors 67 and 68 areconnected so that relay 86 in the cooling relay means 13 energizes a fancontinuously. This function is conventional and does not form a part ofthe present invention but has merely been shown to complete a disclosureof a temperature control system.

The manual switching means 62, in the position shown, vided is acontinuous conduction path between the conductor 60 through bar 63 to aconductor 70. Also provided is a continuous condition path between theconductor 53 and a group of conductors 71, 72 and 73. The conductor 72connects through the bar 64 to a conductor 74 in the position shown toprovide one circuit configuration in the heating mode of operation.

In the cooling mode of operation bar 63 connects conductor 71 toconductor 75 which in turn connects to the cooling relay means 13. Atthe same time bar 64 connects the conductor 59 to conductor 73 for afeedback function that will be described in connection with theoperation of the system.

A fuel valve means 12 which controls the flow of fuel to a burner, notshown, provides the necessary heat during the heating mode of operation.The fuel valve means 12 contains two electrically controllable operatingmeans or solenoids 76 and 77. The solenoid 76 causes the valve to openfrom a full off position to a minimum flow position upon energization ofthe solenoid. The solenoid 77 controls the flow of fuel through valvemeans 12 in a modulating fashion after the solenoid 76 is energized.Solenoid 77 operates in a fashion reverse to that of a normal valve inthat the solenoid 77 when fully energized allows a minimum flow. Theflow through valve means 12 increases to a maximum as the currentthrough solenoid 77 is decreased. The solenoid 76 is connected betweenthe conductor 70 and the conductor 43 while the solenoid 77 is connectedbetween the conductor 74 and a pair of conductors 80 and 81. Conductor88 connects to the power supply means 14 while conductor 81 in turnsupplies power to the cooling relay means 13.

The cooling relay means 13 includes two relays. The first relay 82 has afree-wheeling diode 83 connected across it to protect the transistorcircuitry that energizes the relay 82. Relay 82 is connectedmechanically at 84 to a switch means 85 to in turn control equipmentsuch as a compressor in an off-on fashion as is conventional in coolingequipment. The second relay 86 is connected between the conductor 81 andthe conductor 67 in the subbase means 11 for control of a fan in thecooling equipment. The relay 86 is connected mechanically at 87 to aswitch means 88 for operation of the fan either automatically along withthe relay 82 or manually, in response to the positioning of the switchmeans 65.

The last basic element making up the temperature control system is thepower supply means 14. The power supply means 14 obtains power fromsource 15 through a step-down transformer 90 that has .a primary winding91 and a secondary winding 92. The secondary winding 92 is connectedthrough a diode 93 to a filter capacitor 94 by conductor 95. Thisprovides a filtered direct current power source. In order to completethe filtering a pair of resistors 96 and 97 are provided. To stabilizethe voltages obtained from the power source, a pair of Zener diodes 98and 99 are provided. The Zener diode 98 connects to conductor 43 whilethe Zener diode 99 connects to conductor to provide the output voltagesfor the operation of the system. The stabilized voltage across Zenerdiode 99 is greater than that across Zener diode 98.

OPERATION-HEATING MODE If the temperature control system is assumed tobe in the heating mode of operation with the thermostat satisfied, thereis insuflicient output to transistor 32 between the junctions 30 and 31and transistor 32 is nonconduc tive. Upon a temperature drop, thethermostat means 10 senses this change by the thermistor 23 increasingin resistance. A sufficient voltage difference appears between points 30and 31 and the transistor 32 begins to conduct. The conduction is fromthe supply line 43 through resistor 27 and the emitter-collector portionof the transistor 32 with the current flowing in conductor 33 andthrough the voltage divider output means made up of the resistors 35, 36and 37. The current flow causes a voltage increase across resistors 37and 36. The voltage appearing across resistor 37 progressively turns thetransistor 40 on and allows it to conduct from the conductor 43 to theconductor 44 through anticipator resistor 42. Also, a path can be tracedfrom the power supply conductor 43, through solenoid 76, conductor 70,bar 63, and conductor 60 to the conductor 41. The voltage change thatoccurs across resistor 42 causes a positive feedback to be fed onconductor 55, and resistor 56 to the base of transistor 25. The positivefeedback voltage causes the transistor 40 to conduct even more, and ispurposely made regenerative so as to cause a switching action to occurto pull in or energize the solenoid 76 without any form of modulatingaction. This current flows through the solenoid 76 causes the solenoidto open the fuel valve means 12 to a mimimum flow position allowing fuelto flow to a burner where it is ignited and used to generate heat.

If the temperature in the controlled space further decreases, whichmeans more heat is needed, the bridge is further changed by the changein the value of the thermistor 23 to further increase the conduction oftransistor 32 and thus to increase the voltage drop across the resistor36. The increased drop in voltage across resistor 36 causes thetransistor 45 to begin conduction. This increase in conduction causes anincreased voltage drop to occur across the resistor 47 and the change involtage thus caused is transmitted to the base of transistor 50 causingit to lessen its conduction. The conduction of current throughtransistor 50 is from conductor 80 through solenoid 77, conductor 74,switch bar 64 and conductor 53. Solenoid 77 causes the fuel valve means12 to open to a greater degree as the current drawn through itdecreases. It is thus apparent that as the sensor temperature decreasescalling for more heat, transistor 32 increases conduction which in turncauses a greater voltage drop across resistor 36. This increasesconduction in transistor 45 which in turn decreases conduction intransistor 50. In order to establish a stable and reproduciblemodulating range for transistor 50, a negative feedback circuit isestablished from conductor 53 through resistor 54 to the base oftransistor 25. This negative feedback linearizes" the modulating actionwhich controls the position of the solenoid 77 and also is the principalfactor which determines the throttling range or proportional band inwhich the current in solenoid 77 is proportional to the resistance ortemperature of thermistor 23.

It is obvious that as the temperature rises at the thermostat means andas the thermistor 23 forces the bridge back towards a balanced state,that the modulating transistor circuit means made up of transistors 45and 50 causes the modulation to cease. Further temperature rise willsuddenly and regeneratively render transistor 40 nonconductive so thatthe fuel valve means 12 closes completely.

It will be noted at this point that the cooling relay means 13 providedno function and that the subbase means 11 provided only a connectionbetween the thermostat means 10, the fuel valve means 12, and powersupply means 14. It is obvious that the subbase means 11 and the coolingrelay means 13 could be omitted if only a heating installation wererequired. The functions of these parts could be replaced by directconnections.

OPERATION COOLING MODE If it is desired to operate cooling equipmentwith the control system, it is necessary to move the manual switchingmeans contained in the subbase means 11. This involves moving switchmeans 62 from the heat position to the coo position. In so doing, thebars 63 and 64 move from the position shown to complete contact betweenthe two lower terminals associated with each of the sliding bars. Thefan relay 86 at this time has the ability to be operated either manuallyor automatically depending on the position of switch means 65, and againit is pointed out that this is not material to the present invention.This merely completes the overall system.

In the cooling mode with a space temperature above the control point ofthe thermostat means 10, the transistors 32, 40 and 45 are in anonconductive state. With transistors 40 and 45 nonconductive, thetransistor 50 is conducting fully. Its current conduction path isthrough conductor 81, relay 82, conductor 75, bar 63, conductor 71,conductor 53, and conductor 52. The conduction through relay 82energizes the relay and operates switch means 85 to operate the coolingequipment to lower the temperature in the controlled space.

At this same time, a positive feedback path is provided for transistor50 to make the transistor 50 switch rather than modulate with changes intemperature. The feedback path is through conductor 52, conductor 53,conductor 73, bar 64, conductor 59, resistor 58, conductor 57 to thebase of transistor 24. It is noted that with switch 62 in the coolposition an additional feedback path, yielding positive feedback, isadded from the collector of transistor 50 to the base of transistor 24.The already existing feedback path, from the collector of transistor 50to the base of transistor 25 through resistor 54, yielded negativefeedback as described before. The additional feedback path throughresistor 58 is so proportioned that the overall net feedback is changedfrom negative to positive feedback for the transistor 50'. Changing thefeedback from a negative feedback (usable for modulation) to a positivefeedback (usable for a switching action) is necessary due to the changein the kind of load being controlled. This switching action cleanlyoperates relay 82 to turn on the cooling equipment.

As the cooling equipment controlled by relay 82 is operated, thetemperature at the thermostat means 10 is reduced until the voltagebetween points 30 and 31 causes transistor 32 to conduct. The conductionof transistor 32 in turn causes transistors 40 and 45 to conduct. This 6causes the removal of transistor 50 from conduction and removes the pathfor energization of relay 82 which drops out thereby disconnecting orturning off the cooling equipment.

In the present temperature control system for maintaining a propertemperature in a controlled space, it has been possible to eliminate thenormal moving parts contained in a thermostat by the use of athermistor. By merely changing the net feedback from negative topositive, a function can be obtained that allows the same transistoramplifier means to be used as a modulating system or as a switchingsystem to accomplish the necessary modulation of the fuel valve means 12and the off-on switching of the cooling relay means 13. The use of afeedback circuit also allows for the necessary initial switching actionof transistor 40 to pull in solenoid 76 in an off-on or snap actingfashion to open the fuel valve means 12 to a minimum flow position as isnormally required to cause a burner to operate safely. By the verysimple expedient of a switching means and feedback circuits, it ispossible to obtain both a heating and cooling function without otherauxiliary equipment or moving parts. The present system is exceedinglysimple and compact.

While the feedback circuits in the present device have been shown as ameans of obtaining the modulating and switching action of thetransistors 40, 45 and 50, it would be possible to obtain the necessarymodulating and switching actions by other forms of feedback systems suchas closed loops within the transistor circuitry other than through themeans of the bridge itself. Since this is the case, the applicant doesnot wish to be limited solely to the types of feedback circuits shownand specifically described in the preferred embodiment.

The embodiments of the invention in which an exclusive property or rightis claimed are defined as follows:

1. A heating and cooling temperature control system for a controlledspace, including: means constructed and arranged to sense a temperatureto be controlled including power supply means and thermostat meanshaving temperature responsive circuit means connected to said powersupply means; voltage output means which changes with chanegs intemperature; fuel valve means having a first and a second electricallycontrollable operating means capable of opening said fuel valve means toa minimum flow position and then modulating to a full fiow position;first transistor circuit means having an input connected to said voltageoutput means and an output connected through said first controllableoperating means; said first transistor circuit means further havingpositive feedback circuit means to cause said first transistor circuitmeans to switch and operatively energize said valve means to its minimumflow position; second transistor circuit means having an input connectedto said voltage output means and an output connected through said secondcontrollable operating means; said second transistor circuit meansfurther having negative feedback circuit means to cause said secondtransistor circuit means to operatively energize said valve means in amodulating manner between said minimum flow position and said full flowposition; manual switching means for changing the mode of operation ofsaid system between heating and cooling; relay means connected to saidpower supply means and by said manual switching means to said transistorcircuit means; and second positive feedback circuit means connectedthrough said manual switching means and to said temperature responsivecircuit means so that when said manual switching means is operated tochange the mode of operation to cooling said switching means connectssaid second positive feedback circuit means to said second transistorcircuit means to obtain a switching action to operate said relay means.

2. A temperature control system for a controlled space References Citedas described in claim 1 wherein said t mper re TBSPOH- UNITED STATESPATENTS sive circuit means is bridge circuit means.

3. A temperature control system for a controlled space gompehen asdescribed in claim 23 wherein said feedback circuit 5 4/1568 65 26 meansare circuits from the output means of each of said Velt 1 transistorcircuit means to said bridge circuit means. MEYER PERLIN, PrimaryExaminer 4. A temperature control system for a controlled space asdescribed in claim 3 wherein said positive feedback SUKALO AssistantExammer circuits from said transistor circuit means are connected 10 Us,CL X R to opposite sides of said bridge circuit means. 16526

